The present invention generally relates to apparatus and methods for processing a submerged work surface and particularly relates to apparatus and methods for excluding a liquid from a submerged work surface thereby affording a local dry area around a processing apparatus such as a welding torch, heating device or stress-relieving device.
Processing applications such as welding, thermal stressing and the like in an underwater or submerged environment require a local dry area around the processing head in order that water can be excluded from the work surface to be processed. For example, in welding underwater, the water must be excluded from the molten metal and nearby heated zone to prevent excessive oxidation, premature cooling and other defects. Inert gas is typically used to displace the water locally around the welding head and to provide a chemically inert atmosphere for the molten metal pool. The work surface in many underwater applications, however, is not smooth or regular, particularly after new or unground weld passes have been applied to a work surface. In these cases, a water exclusion device must have sufficient displacement range to fully comply with the highs and lows of and often abrupt changes in the work surface contour.
For welding applications, water displacement around the weld torch and steam displacement from the heated or cold processing area is best achieved at low gas flow rates to avoid known problems at higher flow rates which may be costly to provide, obscure visibility due to excessive bubble formation or disturb the liquid metal pool or other controlled conditions within the local dry zone. However, for large surface contour changes, a higher gas flow rate must be used to maintain sufficient water exclusion if the limited compliance seal has insufficient range and lifts off of the work surface for a portion of its perimeter, or if an annular gas flow only design without a compliant seal is used to displace the water from within the torch inert gas cup. In both cases, the higher flow rate is needed to maintain the minimum required gas velocity across the increased gap, which maintains the minimum pressure differential across the gap to keep the gas flow direction outward into the water, rather than inward with water or mixed phases counterflowing into the welding processing zone. A design combining the benefits of a compliant seal and a gas flow gap may desirably have an increased compliant range relative to either design type alone, however, the combined design will still retain similar problems as each of these design types has individually.
Existing designs for water or other liquid exclusion devices for underwater applications have three basic principles of operation: (1) mechanically sealing the gap between the work surface and the applicator head, e.g., in a welding environment, a cup-shaped gas-filled component around the torch end; (2) flowing gas across the relatively small controlled width gap between the work surface and the applicator head; or (3) providing diverging water/gas cone flowing across a controlled gap to displace water within the contact area of the cone against the work surface. Design variations combining these principles include a gas-permeable compliant seal for multiple concentric flowing water or gas cones. The designs relying on a compliant seal have an inherently limited practical working range because an elastic element is deformed to provide compliance and this element has a limited strain range (before it deforms plastically or is fully compressed), as well as a significantly increasing force requirement for increasing displacement which must be overcome by applicator head manipulation to maintain the desired position along the contoured surface. The force requirement and high displacements may be reduced somewhat by employing thinner or softer deflecting seal elements. However, these thinner elements are increasingly prone to mechanical damage due to inadvertent overloading during use or by tearing during handling operations or while sliding over work surface asperities and discontinuities.
Designs relying on positive water or gas flow through a gap have the limitation that local contour changes or tilting of the applicator head typically generate a differential gap, resulting in the expected differential gas flow around the perimeter of the gap. When the gap is greater in one area, the flow rate and flow velocity of gases, particularly in the case of welding, also becomes greater at the expense of the flow rate and velocity in the remaining areas of the perimeter having a lesser gap. As the flow is reduced in the areas having a lesser gap, the flow rate falls below the minimum required to hold back the water without surging of the water/gas interface or, catastrophically, reverse flow of the water toward the dry welding or process zone within the applicator head housing occurs.
More particularly, existing water exclusion devices are inherently inefficient for use over grooves in the surface of substrates since there is no provision either to limit the flow clearance between the device and the lowest portion of the groove as it is filled or, in the case of xe2x80x9cflow curtainxe2x80x9d types of devices, to provide a differential flow over the groove which is greater than the needed amount away from the groove. As a result, the ability of known devices to exclude water using an internal flow rate below that which disturbs the processing, for example, welding, is limited at best or is ineffective at worst. In addition, the effectiveness of these devices to exclude water from within deep grooves is limited. Even when used within the depth limit of the ability of these devices to exclude water in grooves, they are wasteful of purge fluid since the flow occurring in areas away from the groove is greater than required in order to have sufficient flow over the groove itself. In the worst case, they are totally ineffective to exclude water from deeper grooves.
In accordance with a preferred embodiment of the present invention, there is provided apparatus and methods for excluding liquid, e.g., water, from within a shallow or deep groove formed in submerged substrate materials without excessively high gas flow from within the device. Such high gas flows disturb processing, for example, welding, by chilling or displacing the molten metal pool, or are wasteful of the inert gas commonly used to provide the liquid/gas boundary position at the perimeter of the device. The gas flow must be sufficiently low so as not to disturb the process being applied, yet sufficiently high to effectively displace the surrounding liquid in the gap between the exclusion device and the work surface. Excess liquid vapor must also be prevented from entering the processing zone, which vapor would likely react with the hot or liquid metal and cause weld defects.
To accomplish the foregoing, in a preferred embodiment of the present invention, there is provided a plurality of thin, flat fingers extending parallel to and lying at opposite ends of an exclusion device which is movable along a work surface area such as a groove in the direction of the groove and parallel to the fingers whereby the fingers maintain a differential geometry corresponding to the geometry of the groove adjacent the leading and trailing edges of the exclusion device. Preferably, the thin, flat fingers lie side-by-side at each of the opposite ends of the device and are spring-biased at one end for pivoting movement to an extended position. Consequently, the free or distal ends of each of the fingers is biased in a direction contacting the work surface forming a seal substantially excluding fluid from within the exclusion device. The sides of the device likewise form a seal with the surface straddling the work area or groove. By forming a substantial radius on the distal ends of the fingers, the finger ends will follow the surface contour of the groove under the bias of the springs to form a sufficient mechanical seal with the work surface. The processing head, for example, a welding head, is located within the device between the leading and trailing rows of fingers and a suitable flow of process or purge gas is provided to displace any water from within the controlled clearance space.
In a further preferred embodiment of the present invention, a plurality of blades or fingers extending parallel to one another and to the direction of movement of the exclusion device along the work surface are mounted for translatory movement at the leading and trailing edges of the exclusion device. Particularly, the translatory fingers are generally elongated in the direction of movement and have spaced vertical slots for mounting the fingers on a pair of guide rods extending transverse to the direction of movement of the device. A spring, preferably having a central transversely extending beam and forwardly and rearwardly extending leaf springs, seals against an upper portion of the housing with the distal ends of the springs engaging upper surfaces of the fingers, biasing the fingers in a downward direction to contact the work surface. It will be appreciated that the fingers not only may translate vertically but can be canted about transverse axes to accommodate irregularities in the work surface. Thus, the lower elongated surfaces of the fingers engage the work surface, forming a seal substantially excluding fluid from within the housing. The gaps between the translatory blades as well as between the leaf springs are sufficiently small that the gas pressure within the exclusion device prevents fluid leakage into the exclusion area.
In a still preferred form of the present invention, the processing apparatus, for example, the welding head or torch, is coupled to the water exclusion device through a spring-biased bellows whereby relative motion between the torch head and the exclusion device along the torch axis is provided. The bellows spring loads the exclusion device housing against the work surface. It will be appreciated that, in use, the torch head is attached to a manipulator or robotic arm which provides the reaction force for maintaining the exclusion device against the work surface under the bias of the bellows spring. Thus, using either the pivoted or translatory fingers previously discussed, the torch head can be maintained in position relative to the work surface. For example, in automated arc voltage controlled welding devices, it is desirable to maintain a constant voltage between the welding head and the work surface. This is typically maintained by a servocontrol responsive to measurements of the voltage drop across the arc between the torch head and work surface. Consequently, the torch head can be motor-driven to drive the torch head toward or away from the work surface while maintaining the work surface free of fluid by the use of compliant seals, the pivoted or translatory fingers and the higher gas pressure within the exclusion device.
In a preferred embodiment according to the present invention, there is provided apparatus for processing a submerged work surface including a groove, comprising a closed housing having an opening and movable relative to the work surface, an array of discrete fingers carried by the housing for pivotal movement substantially independently of one another and generally about parallel axes between retracted positions and positions extending from the housing at locations about at least a portion of the opening, the fingers having tips at distal ends thereof spaced from the axes for engaging or lying in close proximity to the groove in the extended positions of the fingers, means for pivoting the fingers into the extended positions thereof substantially independently of one another enabling the tips of the fingers to follow the groove of the work surface as the housing is displaced relative to the surface and a working head carried by the housing and interiorly of the fingers for processing the surface through the opening.
In a further preferred embodiment according to the present invention, there is provided apparatus for processing a submerged work surface including a groove, comprising a closed housing having an opening and movable relative to the work surface, an array of discrete fingers carried by the housing in side-by-side relation to one another for translational movement substantially independently of one another between retracted positions and positions extending from the housing at locations about at least a portion of the opening, the fingers being elongated in a direction generally normal to the direction of translatory movement and having long edges for engaging or lying in close proximity to the groove in the extended positions of the fingers, means for displacing the fingers into the extended positions thereof substantially independently of one another enabling the edges thereof to follow the groove of the work surface as the housing is displaced relative to the surface and a working head carried by the housing and interiorly of the fingers for processing the surface through the opening.
In a still further preferred embodiment according to the present invention, there is provided apparatus for processing a submerged work surface including as groove, comprising a closed housing having an opening and movable relative to the work surface, an array of discrete fingers carried by the housing for movement substantially independently of one another between retracted positions and positions extending from the housing at locations about at least a portion of the opening, the fingers having surfaces for engaging or lying in close proximity to the groove in the extended positions thereof, means for displacing the fingers into the extended positions thereof substantially independently of one another, enabling the surfaces to follow the groove of the work surface as the housing is displaced relative to the surface and a working head mounted on the housing for movement relative to the housing in directions toward and away from the housing.
In a still further preferred embodiment according to the present invention, there is provided in a device for processing a groove of a submerged work surface wherein the device includes a closed housing, an opening, a working head carried by the housing and an array of discrete fingers carried for pivotal movement substantially independently of one another between retracted positions and positions extending from the housing about at least a portion of the opening, a method for excluding fluid from the work surface, comprising the steps of pivoting the fingers substantially independently of one another relative to the housing enabling tips of the fingers to engage in the groove in extended positions thereof, advancing the device along the work surface with the fingers following the contour of the groove and movable independently of one another to substantially exclude fluid from the work surface exposed to the working head within the housing and operating the working head to process the work surface through the opening as the device is advanced along the work surface with the fingers in continuous engagement along the work surface.
In a still further preferred embodiment according to the present invention, there is provided in a device for processing a groove of a submerged work surface wherein the device includes a closed housing, an opening, a working head carried by the housing and an array of elongated discrete fingers carried for translatory movement substantially independently of one another between retracted positions and positions extending from the housing about at least a portion of the housing to engage a long surface thereof along the groove of the work surface, a method for excluding fluid from the work surface, comprising the steps of translating the fingers substantially independently of one another relative to the housing enabling the long surfaces of the fingers to engage in the groove in extended positions thereof, advancing the device along the work surface with the fingers following the contour of the groove and movable independently of one another to substantially exclude fluid from the work surface exposed to the working head within the housing and operating the working head to process the work surface through the opening as the device is advanced along the work surface with the fingers in continuous engagement along the work surface.
In a still further preferred embodiment according to the present invention, there is provided in a device for processing a groove of a submerged work surface wherein the device includes a closed housing, an opening, a working head coupled to the housing and an array of discrete fingers carried for movement substantially independently of one another between retracted positions and positions extending from the housing about at least a portion of the opening, a method for excluding fluid from the work surface, comprising the steps of extending the fingers substantially independently of one another relative to the housing enabling surfaces of the fingers to engage in the groove in extended positions thereof, advancing the device along the work surface with the fingers following the contour of the groove and movable independently of one another to substantially exclude fluid from the work surface exposed to the working head within the housing, operating the working head to process the work surface through the opening as the device is advanced along the work surface with the fingers in continuous engagement along the work surface and providing for relative movement between the working head and the housing.